US20110051456A1 - Lighting device employing a light guide plate and a plurality oflight emitting diodes - Google Patents
Lighting device employing a light guide plate and a plurality oflight emitting diodes Download PDFInfo
- Publication number
- US20110051456A1 US20110051456A1 US12/445,328 US44532807A US2011051456A1 US 20110051456 A1 US20110051456 A1 US 20110051456A1 US 44532807 A US44532807 A US 44532807A US 2011051456 A1 US2011051456 A1 US 2011051456A1
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- Prior art keywords
- array
- leds
- lens
- led
- guide plate
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Classifications
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
- G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
- G02B6/0013—Means for improving the coupling-in of light from the light source into the light guide
- G02B6/0015—Means for improving the coupling-in of light from the light source into the light guide provided on the surface of the light guide or in the bulk of it
- G02B6/002—Means for improving the coupling-in of light from the light source into the light guide provided on the surface of the light guide or in the bulk of it by shaping at least a portion of the light guide, e.g. with collimating, focussing or diverging surfaces
- G02B6/0021—Means for improving the coupling-in of light from the light source into the light guide provided on the surface of the light guide or in the bulk of it by shaping at least a portion of the light guide, e.g. with collimating, focussing or diverging surfaces for housing at least a part of the light source, e.g. by forming holes or recesses
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
- G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
- G02B6/0013—Means for improving the coupling-in of light from the light source into the light guide
- G02B6/0015—Means for improving the coupling-in of light from the light source into the light guide provided on the surface of the light guide or in the bulk of it
- G02B6/002—Means for improving the coupling-in of light from the light source into the light guide provided on the surface of the light guide or in the bulk of it by shaping at least a portion of the light guide, e.g. with collimating, focussing or diverging surfaces
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
- G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
- G02B6/0013—Means for improving the coupling-in of light from the light source into the light guide
- G02B6/0023—Means for improving the coupling-in of light from the light source into the light guide provided by one optical element, or plurality thereof, placed between the light guide and the light source, or around the light source
- G02B6/0031—Reflecting element, sheet or layer
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
- G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
- G02B6/0066—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form characterised by the light source being coupled to the light guide
- G02B6/0068—Arrangements of plural sources, e.g. multi-colour light sources
Abstract
The present invention relates to a lighting device (10). The device comprises a light guide plate (12), and at least one array (14) of light emitting diodes (LEDs) (16), which LEDs are accommodated in holes (20) arranged in the light guide plate. The device is characterized by an array (24) of lenses (26) arranged such that light emitted by the LEDs passing the lens array is at least partly directed towards areas (28) of the light guide plate free from holes.
Description
- The present invention relates to lighting device comprising a light guide plate and at least one array of light emitting diodes.
- Progress in the brightness, lumen efficacy and affordability of solid state light sources such as light emitting diodes (LEDs) enables new lighting applications that are no longer restricted to niche markets. LEDs offer several advantages over traditional light sources, such as long lifetime, low operating voltage, instant on, etc. For these and other reasons, LEDs are becoming more and more suited for making lamps for several applications such as color variable lamps, spotlights, LCD backlighting, architectural lighting, stage lighting, etc.
- For many lighting applications, the light of a single LED is not sufficient, and light of multiple LEDs needs to be combined to form a light source. One solution is to mix light of multiple LEDs in a light guide, before the light leaves the lighting device. An example of such a solution is disclosed in the document “LED Backlight designs using Luxeon high flux light source solutions” by Lumileds, Seattle 2004, http://www.lumileds.com/pdfs/Luxeon_light_source_solutions.pdf. A backlight based on side-emitting LEDs described in this document is schematically illustrated in
FIGS. 1 a-1 b. With reference toFIGS. 1 a-1 b, thebacklight 100 comprises alight guide 102 provided with cylindrical throughholes 104 which are arranged in a linear array along anedge 106 of the light guide. In each through hole, there is provided a side-emittingLED 108, whereby light from the LEDs is coupled into the light guide through the sidewall of the through holes, as illustrated byexemplary ray traces 110. Theedge 106 is preferably reflective, to avoid unintended out-coupling of light via the edge. - However, in such a solution when a dense array of
LEDs 108 is placed close to theedge 106 it may occur that light from oneLED 108 a is directed via reflection off the edge 106 (exemplary ray trace 112) towards anothernearby hole 104 b and gets absorbed or scattered at theLED 108 b inside this hole. Thus, the lumen efficiency of such a lighting device is degraded. - It is an object of the present invention to overcome or at least alleviate this problem, and to provide a lighting device with improved lumen efficiency.
- This and other objects that will be apparent from the following description are achieved by means of a lighting device, according to the appended claim 1, comprising a light guide plate and at least one array of light emitting diodes (LEDs), which LEDs are accommodated in holes arranged in the light guide plate, characterized by an array of lenses arranged such that light emitted by the LEDs passing the lens array is at least partly directed towards areas of the light guide plate free from holes.
- Because of the lens array, no or little light strikes the nearby holes. Therefore, the LEDs can be placed closer together and losses due to absorption or scattering at nearby LEDs in the lighting device are diminished. Overall, the luminous efficiency and power of the lighting device can be increased.
- Preferably, the lens array comprises at least one row of positive lenses, to readily direct the light in the wanted directions. Also preferably, the lens pitch is about ½ of the LED pitch, which provides to a feasible design of the lighting device.
- In one embodiment, the lens array is placed between one LED array and a reflective edge of the light guide plate such that light emitted by the LEDs in the array and reflected by the reflector is directed by the lens array to pass between the LEDs in the array. Thereby, losses due to absorption or scattering at adjacent LEDs/holes in the array are diminished, and the luminous efficiency of the lighting device is increased. To further boost these effects, the LEDs are preferably aligned with every second junction between two adjacent lenses in the lens array.
- In another embodiment, the lens array is placed between a first LED array and a second LED array such that light emitted by the LEDs in the first array and passing the lens array is directed by the lens array to pass between the LEDs in the second array. Thereby, losses due to absorption or scattering at LEDs/holes in the nearby array are diminished, and the luminous efficiency of the lighting device is increased. To further boost these effects, the distance between the first LED array and the lens array and the distance between the second LED array and the lens array are preferably equal. Further, the LEDs of the first array may be aligned with the optical axes of every second lens in a row of the lens array while the LEDs of the second array may be aligned with the optical axes of every other second lens in the row of the lens array. Alternatively, the LEDs may be aligned with every second junction between two adjacent lenses in a row of the lens array.
- Preferably, the holes are cylindrical holes, and the LEDs are preferably side emitting LEDs, for useful in-coupling of light into the light guide plate.
- This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing currently preferred embodiments of the invention.
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FIG. 1 a is a top view of a backlight according to prior art. -
FIG. 1 b is a cross-sectional side view of the backlight ofFIG. 1 a. -
FIG. 2 is a partial top view of a lighting device according to a first embodiment of the invention. -
FIG. 3 is a partial top view of a lighting device according to a first variant of a second embodiment of the invention. -
FIG. 4 is a partial top view of a lighting device according to a second variant of the second embodiment of the invention. - A light emitting diode (LED) based lighting device according to a first embodiment of the present invention will now be described with reference to
FIG. 2 . - The lighting device denoted 10 comprises a
light guide plate 12. Thelight guide plate 12 is transparent and can be made of glass or plastics (such as PMMA or PC), for example. - The
lighting device 10 further comprises alinear array 14 ofLEDs 16 arranged along areflective edge 18 belonging to thelight guide plate 12. Thereflective edge 18 serves to direct any incident light back into thelight guide plate 12, to avoid unintentional out-coupling of light from thelight guide plate 12 via the edge. TheLEDs 16 are preferably side-emitting omnidirectional LEDs. - The
LEDs 16 are accommodated in cylindrical holes 20 having a circular lateral cross-section, which holes 20 are arranged in thelight guide plate 12. ‘Lateral’ is in relation to the plane of the light guide plate. Each hole 20 has a circumferential side facet (cylinder wall) 22 through which light from the accommodatedLED 16 is to be laterally coupled into thelight guide plate 12. The holes 20 could be through holes or holes having an opening towards one side of thelight guide plate 12 only. - According to the invention, the
lighting device 10 further comprises alens array 24. Thelens array 24 is placed between thereflective edge 18 and theLED array 14, and it comprises one linear row ofpositive lenses 26. Thelenses 26 may be formed separately or as integral parts of thelight guide plate 12. Any gap between thelenses 26 and thereflective edge 18 can be filled with air, for example. Thelens array 24 serves to direct light emitted from theLEDs 16 and reflected off theedge 18 towards areas of thelight guide plate 12 free from or with no holes 20 (orLEDs 16, consequently). Namely, the light is directed to pass between theLEDs 16. To this end, in a preferred embodiment, the lens pitch P1 is ½ of the LED pitch P2(P1=½* P2), and with everysecond junction 30 between twoadjacent lenses 26 in thelinear lens array 24 there is aligned anLED 16. The LED pitch P2 is the distance between the centers of twoadjacent LEDs 16, and “aligned with” means here that an imaginary line from thejunction 30, which line is perpendicular to the main linear direction of the lens array, runs through the center of aLED 16. Further, the focal strength of alens 26 should satisfy the following relation 1/f=1/D, where f is the focal length and D is the distance between theLED array 14 and the lens array 24 (the total lens strength ftot is formed by passing throughlens 26 twice; 1/ftot=1/f+1/f=2/f and 1/ftot=1/D+1/D=2/D; hence 1/f=1/D). The focal length f is given by f=(n/(n-1))R1, where n is the refractive index of the material of thelight guide plate 12 and R1 is the radius of eachlens 26. The refractive index for PMMA is typically about 1.49 and the refractive index for PC is typically about 1.56. The various parameters mentioned above should be chosen such that lens radius R1 is larger than ½ of the lens pitch P1(R1>½* P1), otherwise thelens array 24 cannot be realized. Also, to avoid too curved lens surfaces, which can be difficult to make, the parameters should preferably be chosen such that R1>½* P1 is by far not violated. In a feasible design, the radius of thecylindrical holes 18 is 3 mm and the LED pitch P2 is 9 mm. The lens pitch P1 is half the LED pitch P2, that is P1=4.5 mm. For example, when D=15, the lens radius R1 becomes D*(n-1)/n=5 mm, which is larger than half the lens pitch P1, whereby R1>½* P1 is satisfied. - Upon operation of the
lighting device 10, alight ray 32 emitted by theLED 16 a, which lightray 32 otherwise would have been reflected off theedge 18 an into theadjacent hole 20 b (as inFIG. 1 a), is focused by a correspondinglens 26 of thelens array 24 on its way towards thereflective edge 18. After reflection off theedge 18, thelight ray 32 is again focused by the correspondinglens 26 towards thespace 28′ between theholes hole 20 b. On the other hand, the direction of alight ray 34 emitted by theLED 16 a, which lightray 34 otherwise would have been reflected off theedge 18 towards thespace 28″ between theholes lens array 24 since thelight ray 34 passes close to the optical axis of the lens 26 (whereas thelight ray 32 passes thelens 26 off-axis and is refracted more strongly). Therefore, thelight ray 34 is still directed towards thespace 28″ between theholes adjacent LEDs 16. Overall, thelens array 24 serves to image reflections of theLEDs 16 atspaces 28 between thereal LEDs 16 b, whereby losses due to absorption or scattering at adjacent LEDs are diminished, and the luminous efficiency of thelighting device 10 is increased. - A lens array can also advantageously be used in a second embodiment, wherein two LED arrays are arranged parallel to each other, as illustrated in
FIGS. 3-4 . The function of the lens array is here to avoid that light from one array is absorbed or scattered at LEDs in the other array. - In a first variant (
FIG. 3 ) of the second embodiment, the lighting device denoted 10 comprises alight guide plate 12. Thelight guide plate 12 should be transparent and can be made of glass or plastics (such as PMMA or PC), for example. - The
lighting device 10 further comprises two parallellinear arrays 14 ofLEDs 16. TheLEDs 16 are preferably side-emitting omnidirectional LEDs. - The
LEDs 16 are accommodated in cylindrical holes 20 having a circular lateral cross-section, which holes 20 are arranged in thelight guide plate 12. Each hole 20 has a circumferential side facet (cylinder wall) 22 through which light from the accommodatedLED 16 is to be coupled into thelight guide plate 12. The holes 20 could be through holes or holes having an opening towards one side of thelight guide plate 12 only. - According to the invention, the
lighting device 10 further comprises alens array 24 arranged in thelight guide plate 12. Thelens array 24 is placed between the twoLED arrays 14 in an in-plane arrangement. Thelens array 24 is formed by cutting or otherwise removing aportion 36 of thelight guide plate 12, whichportion 36 has the form of a linear array of biconcave or double concave lenses. Left is alinear lens array 24 with two rows of opposingpositive lenses 26. Thelens array 24 serves to direct light emitted from theLEDs 16 in one array and passing thelens array 24 towards areas of thelight guide plate 12 free from or with no holes 20 (orLEDs 16, consequently). Namely, the light is directed to pass between theLEDs 16 of the other array. To this end, in a preferred embodiment, the lens pitch P1 is ½ of the LED pitch P2(P1=½*P2), the distance Da between theLED array 14 a and thelens array 24 and the distance Db between the LED array 14 b and thelens array 24 are equal (Da=Db), and theLEDs 16 a ofarray 14 a are aligned with theoptical axes 38 a of everysecond lenses 26 of a row while theLEDs 16 b of array 14 b are aligned with theoptical axes 38 b of every othersecond lenses 26 of the row (thus, the twoarrays 14 a and 14 b are displaced with half a LED pitch P2 in relation to each other). Further, the focal strength of two opposinglenses 26 should satisfy the following relation 1/f=1/Da+1/Db, where f is the focal length. The focal length f is given by f=(½)(n/(n-1))R1, where n is the refractive index of the material of thelight guide plate 12 and R1 is the radius of eachlens 26. The refractive index for PMMA is typically about 1.49 and the refractive index for PC is typically about 1.56. The various parameters mentioned above should be chosen such that lens radius R1 is larger than ½ of the lens pitch P1(R1>½* P1), otherwise thelens array 22 cannot be realized. Also, to avoid too curved lens surfaces, which can be difficult to make, the parameters should preferably be chosen such that R1>½* P1 is by far not violated. In a feasible design, the radius of thecylindrical holes 18 is 3 mm and the LED pitch P2 is 9 mm. The lens pitch P1 is half the LED pitch P2, that is P1=4.5 mm. For a system with Da=Db=15, the lens radius R1 becomes 5 mm, which is larger than half the lens pitch P1, whereby R1>½* P1 is satisfied. - Upon operation of the
lighting device 10, a light beam 40 emitted by theLED 16 a′, which light beam 40 otherwise at least partly would have struck at least onehole 20 b in the adjacent LED array 14 b, is focused by two opposinglenses 26 in thelens array 24 such that theLED 16 a′ is imaged atspace 28 b′ between twoholes 20 b in array 14 b. Consequently, the beam 40 misses theholes 20 b in the LED array 14 b. Similarly, alight beam 42 is focused bylens array 24 imaging theLED 16 a′ atspace 28 b″, and so on. Overall, thelens array 24 serves to image theLEDs 16 a of onearray 14 a atspaces 28 b between theLEDs 16 b of the other array 14 b, and vice versa, whereby losses due to absorption or scattering at LEDs in the nearby array are diminished, and the luminous efficiency of thelighting device 10 is increased. - In a second variant (
FIG. 4 ) of the second embodiment, theLEDs 16 are aligned with everysecond junction 30 between twoadjacent lenses 26 in a row of thelens array 22. Here alight beam 44 emitted by theLED 16 a′ is focused by two opposinglenses 26 in thelens array 24 such that theLED 16 a′ is imaged atspace 28 b′ between twoholes 20 b in array 14 b. Consequently, thebeam 44 misses theholes 20 b in the LED array 14 b. Similarly, alight beam 46 is focused bylens array 24 imaging theLED 16 a′is atspace 28 b″, and so on. - The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, in the first embodiment, instead of a straight reflective edge and linear LED array, the LEDs could be arranged in a curved array along a curved reflective edge, given that the radius of the curvature is considerably larger than the LED pitch. In the second embodiment, the lens array could comprise only one row of positive lenses. This requires that the lenses are more curved. In both the first and second embodiments, the LED pitch-lens pitch ratio could be different, for example 1:1. Also, the first and second embodiments could be combined in a single device comprising several parallel LED arrays, one of which is placed along a reflective edge of the light guide plate.
Claims (11)
1. A lighting device, comprising:
a light guide plate defining a plurality of holes,
at least one array of light emitting diodes (LEDs) at least partially disposed in the holes; and,
an array of lenses arranged such that light emitted by the LEDs passing said lens array is at least partly directed towards areas of the light guide plate free from holes.
2. A device according to claim 1 , wherein the array of lenses comprises at least one row of positive lenses.
3. A device according to claim 1 , wherein the lens pitch (P1) is about ½ of the LED pitch (P2).
4. A device according to claim 1 , wherein the lens array is placed between one LED array and a reflective edge of the light guide plate such that light emitted by the LEDs in the array and reflected by the reflector is directed by the lens array to pass between the LEDs in the array.
5. A device according to claim 4 , wherein the LEDs are aligned with every second junction between two adjacent lenses in the lens array.
6. A device according to claim 1 , wherein the lens array is placed between a first LED array and a second LED array such that light emitted by the LEDs in the first array and passing the lens array is directed by the lens array to pass between the LEDs in the second array.
7. A device according to claim 6 , wherein the distance (Da) between the first LED array and the lens array and the distance (Db) between the second LED array and the lens array are equal.
8. A device according to claim 6 , wherein the LEDs of the first array are aligned with the optical axes of every second lens in a row of the lens array while the LEDs of the second array are aligned with the optical axes of every other second lens in the row of the lens array.
9. A device according to claim 6 , wherein the LEDs are aligned with every second junction between two adjacent lenses in a row of the lens array.
10. A device according to claim 1 , wherein the holes are cylindrical holes.
11. A device according to claim 1 , wherein the LEDs are side emitting LEDs.
Applications Claiming Priority (7)
Application Number | Priority Date | Filing Date | Title |
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EP06122321 | 2006-10-16 | ||
EP06122321.0 | 2006-10-16 | ||
EP06122321 | 2006-10-16 | ||
EP07100361 | 2007-01-11 | ||
EP07100361.0 | 2007-01-11 | ||
EP07100361 | 2007-01-11 | ||
PCT/IB2007/054166 WO2008047285A1 (en) | 2006-10-16 | 2007-10-12 | Lighting device |
Publications (2)
Publication Number | Publication Date |
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US20110051456A1 true US20110051456A1 (en) | 2011-03-03 |
US8083390B2 US8083390B2 (en) | 2011-12-27 |
Family
ID=39125592
Family Applications (2)
Application Number | Title | Priority Date | Filing Date |
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US12/445,328 Expired - Fee Related US8083390B2 (en) | 2006-10-16 | 2007-10-12 | Lighting device employing a light guide plate and a plurality of light emitting diodes |
US13/312,101 Abandoned US20120075884A1 (en) | 2006-10-16 | 2011-12-06 | Lighting device employing a light guide plate and a plurality of light emitting diodes |
Family Applications After (1)
Application Number | Title | Priority Date | Filing Date |
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US13/312,101 Abandoned US20120075884A1 (en) | 2006-10-16 | 2011-12-06 | Lighting device employing a light guide plate and a plurality of light emitting diodes |
Country Status (5)
Country | Link |
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US (2) | US8083390B2 (en) |
EP (1) | EP2082166A1 (en) |
JP (1) | JP5215312B2 (en) |
TW (1) | TW200834011A (en) |
WO (1) | WO2008047285A1 (en) |
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US20140218968A1 (en) * | 2013-02-05 | 2014-08-07 | National Central University | Planar lighting device |
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CN102102817A (en) * | 2009-12-22 | 2011-06-22 | 株式会社住田光学玻璃 | Light-emitting device, light source and method of manufacturing the same |
JP2011238366A (en) * | 2010-05-06 | 2011-11-24 | Funai Electric Co Ltd | Plane light-emitting device |
US20130163272A1 (en) * | 2011-12-23 | 2013-06-27 | Touchsensor Technologies, Llc | User interface lighting apparatus |
TWI476350B (en) | 2012-03-21 | 2015-03-11 | Young Lighting Technology Inc | Light source module |
JP2016162714A (en) * | 2015-03-05 | 2016-09-05 | セイコーエプソン株式会社 | Luminaire, display device and portable electronic equipment |
JP7239042B2 (en) * | 2019-03-07 | 2023-03-14 | オムロン株式会社 | Light-emitting device and vehicle lamp |
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Also Published As
Publication number | Publication date |
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JP2010507191A (en) | 2010-03-04 |
TW200834011A (en) | 2008-08-16 |
JP5215312B2 (en) | 2013-06-19 |
EP2082166A1 (en) | 2009-07-29 |
WO2008047285A1 (en) | 2008-04-24 |
US20120075884A1 (en) | 2012-03-29 |
US8083390B2 (en) | 2011-12-27 |
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